2019-09-042019-09-042012PEREIRA, Nayan Cezar dos Santos. Estudo isotópico (Pb-Pb e Sm-Nd) de rochas félsicas do baixo rio iriri, domínio iriri- Xingu, província amazônia central, centro do Pará. Orientador: Moacir José Buenano Macambira. Coorientador: Marcelo Lacerda Vasquez. 2012. 86 f. Trabalho de Curso (Bacharelado em Geologia) - Faculdade de Geologia, Instituto de Geociências, Universidade Federal do Pará, 2012. Disponível em http://bdm.ufpa.br/jspui/handle/prefix/1971:. Acesso em:.http://bdm.ufpa.br/jspui/handle/prefix/1971The studied area belongs to the southern portion of the Xingu-Iricoumé Block, located in the Central Amazonia Province, which is the oldest portion of the Amazonian Craton. In the study area three lithological units were identified: the A-type Undifferentiated Granite (clinopyroxene-bearing quartz-syenite and biotite-bearing inequigranular syenogranites), I-type Undifferentiated Granite (porphyritic quartz-monzodiorites, leucoquartz-monzonite and biotite-bearing inequigranular monzogranites) and volcanic rocks identified as Iriri Group (microgranodiorite, porphyritic dacites, porphyritic andesite, biotie-bearing porphyritic quartz-latite and dacitic ignimbrite), the latter occupies the largest surface of the study area. This study included field words, accompanied by rock sampling. Furthermore, petrographic study of 33 representative samples from the three units and Pb-evaporation and Sm-Nd isotopic analysis were carried on. Geochronological data distinguishes two different magmatic periods in the study area. The first one, ca. 1986 Ma, is represented by a 1986 ± 4 Ma quartz-monzonite and a 1986 ± 1 Ma monzogranite, both belonging to the I-type Granites, and a 1987 ± 3 Ma dacite of Iriri Group. The second period of 1889 ± 3 Ma is represented by quartz-syenite which belongs to A-type Granites. The Sm-Nd results indicate for I-type Granites and Iriri Group, TDM model ages between 2.6 and 2.4 Ga and εNd(t) = -5.3 to -2.8, which suggest an Archean crust contribution younger than that for A-type Granites with TDM = 2.9 Ga and εNd (t) = -8.8. The age here obtained for the Iriri Group conflicts with the previous ages admitted for the group elsewhere. However, as recent dating on volcanic rocks collected close to the Iriri Group area-type yielded a similar age, we suggest that the term Iriri Group should be used to predominantly felsic volcanic and vulcanoclastic rocks aged of 1987 Ma. Concerning the geochronological provinces, it is considered that the study area belongs to the Central Amazonia Province and the limit between this province and Ventuari-Tapajós Province is located westward.Acesso AbertoGeologia IsotópicaEvolução crustalRochas félsicasProvíncia Amazônia CentralCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIATrabalho de Curso - Graduação - Monografia